Neural control of muscle movements in feeding behavior

本研究的主要目的是了解神经系统简单的海兔摄食行为的神经机制。特定部位的闭口肌(JC)由兴奋性(JC)和抑制性运动神经元(MAL)双重支配，分别释放谷氨酸(Glu)和乙酰胆碱(ACh)。另一方面，红束闭合肌肉由胆碱能兴奋性运动神经元支配。本研究的目的是了解产生连接电位的受体和通道的特点，以及中枢神经元对其功能的调控机制。用木瓜蛋白酶分离肌纤维，对分离的单个肌细胞进行全细胞膜片钳，研究与ACh或Glu受体相关的离子机制。电泳法ACh使JC肌细胞超极化，而Glu使JC肌细胞去极化，提示JC肌单细胞膜上ACh受体和Glu受体共存。在不同的正负离子组成的吸管溶液中的实验表明，ACh在JC肌细胞中的反应是由氯离子电流引起的，而在ARC肌细胞中的反应是由Na+和部分K+电流引起的。这些结果表明，ACh受体在JC肌细胞上与Cl~-通道有关，在ARC肌细胞上与Na~+和K~+离子通透通道有关。本文还探讨了海兔神经元和肌肉中广泛存在的多肽(FMRF、Myomodrin A、SCP_A)对抑制性连接电位(IJPs)的影响。这些多肽的应用减少了JC肌肉纤维因MAL燃烧而产生的IJP的大小。在全细胞钳制实验中，FMRF可降低ACh诱导的氯离子电流，提示FMRF可调节ACh受体通道的功能。

Major goal of our research is to know the neural mechanism generating feeding behavior in Aplysia which has simple nervous system. Jaw-closing (JC) muscle in a specific portion is doubly innervated by excitatory (JC) and inhibitory motor neurons (MAl) , which release glutamate (Glu) and acetylcholine (ACh) , respectively. On the other hand, redula-closer (ARC) muscle is innervated by cholinergic excitatory motor neurons. The purpose of this research is to know the characteristics the receptor and channels producing junction potentials, and also the modulatory mechanism of their function by central neurons. The muscle fibers were dissociated by using papain, and whole-cell patch clamp was performed on isolated single muscle cells to study the ionic mechanism associated with ACh or Glu reception. Iontophoretically applied ACh hyperpolarized the JC muscle cells while applied Glu depolarized the same cells, suggesting that ACh and Glu receptors coexist on the membrane of the single cell in the JC muscle. The experiments with different cation and anion compositions in the pipette solution showed that ACh-induced response in the JC muscle cells is caused by Cl^- currents while the response in the ARC muscle cells is cause by Na^+ and partly K^+ currents. These results suggest that the ACh receptors associated with a Cl^- channel in the JC muscle cells, and with a cation channel permeable to both Na+ and K+ in the ARC muscle cells. The effects of peptides (FMRF,Myomodulin A,SCP_A) widely found in Aplysia neurons and muscles on the inhibitory junction potentials (IJPs) were also explored. Application of these peptides reduced the size of IJPs produced in the JC muscle fibers by the MAl firing. In the whole cell clamp experiments, FMRF reduced Cl^- current induced by ACh application, suggesting that FMRF can modulate the function of ACh receptor channels.